1. Field of the Invention
This invention relates to a method for welding a metal honeycomb carrier in which the metal honeycomb carrier for a catalyst convertor is welded.
2. Description of the Prior Art
Generally, to clean automobile exhaust, the automobile exhaust system is provided with a metal honeycomb carrier as disclosed in the Japanese Patent Application Laid-open No. 54-13462.
FIG. 7 shows the details of such a metal honeycomb carrier. This metal honeycomb carrier is formed by alternatively piling metal corrugated plate 11 and flat plate 13 and rolling the piled plates into a multiple form with a core material at the center, thereby providing a core section 17.
In this core section 17, when the corrugated plate 11 and the flat plate 13 are kept as rolled, flow of exhaust into the core section 17 causes the corrugated plate 11 and the flat plate 13 arranged at the center of the core section 17 to protrude in the axial direction of the core section 17, causing so-called film out phenomenon. To remedy this, the corrugated plate 11 and the flat plate 13 are mutually welded after the core section 17 is formed.
FIG. 8 shows one example of existing methods for welding a metal honeycomb carrier. In this method, with one end surface 19 of the core section 17 upside, laser beam 23 is radiated to the end surface 19 from a welding head 21 which is disposed above the end surface 19. The welding head 21 is moved in the radial direction of the core section 17 to weld the corrugated plate 11 and the flat plate 19 at the end surface 19 which is exposed to the laser beam 23.
But, in this conventional method of welding the honeycomb carrier, to weld with the laser beam 23 focused on the end surface 19 of the core section 17, the laser beam 23 spotted on the end surface 19 has a small diameter of about 0.2 mm for example. Therefore, to weld the plates with 2-mm width of 2 mm, the welding head 21 must go and return 5 times, entailing a disadvantage of consuming a great time for welding.
To remedy this disadvantage, the end surface 19 of the core section 17 is approached to the welding head 21 from the focal point of the laser beam 23 so as to be welded with the laser beam 23 having relatively greater diameter. But, the power density differs between the center and peripheral portions of the laser beam 23, resulting in causing a drawback that it is difficult to uniformly weld the end surface 19.